Experimental investigation of the effects of polarization on the measured radiation efficiency of a dielectric resonator antenna

©2008 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.The radiation efficiencies of two rectangular dielectric resonant antennas (DRAs) were investigated using the directivity/ gain (D/G) method and the Wheeler cap method. Both antennas are linearly polarized but have different linear polarization purities. Through comparison of their radiation efficiencies, itpsilas shown that the polarization purity strongly affects the D/G measurement of the DRAspsila radiation efficiency.Qinghua Lai, Georgios Almpanis, Christophe Fumeaux, Hansruedi Benedickter, and Rüdiger Vahldiec

Near-field radiation pattern distortion of antenna attached to wall in through-the-wall radar imaging

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Near-field radiation pattern distortion of antenna attached to wall in through-the-wall radar imaging

ISSN:1684-996

An active tagging system using circular-polarization modulation

An active read/write microwave tagging system using circular-polarization modulation as a novel modulation scheme for radio-frequency identification systems is presented. The proposed modulation scheme reduces demodulation complexity and power consumption on the battery-powered tag. Additional coding of the circular-polarization modulated data reduces transmission errors due to polarization inversion at multipath propagation. In multiple-reader environments, the main jamming threat occurs from power carriers of different interrogators. A combination of circular-polarization modulation and frequency hopping is presented that shows an increased immunity against multipath phenomena for multiple-tag and multiple-reader environments

Comparison of the Radiation Efficiency for the Dielectric Resonator Antenna and the Microstrip Antenna at Ka Band

The radiation efficiency of a dielectric resonator antenna (DRA) and a microstrip antenna (MSA) at Ka band is investigated numerically and experimentally. For direct comparison, one cylindrical DRA and one circular disk MSA were designed with similar feeding networks for operation at around 35 GHz. The efficiency of both devices was measured using the directivity/gain (D/G) method and the Wheeler cap method, in both of which the losses in the test system and the feeding structure were taken into account for calibration purposes. A good agreement between measured and simulated results for both methods is found, when considering the effect of the sampling interval and cross-polarization in the D/G method and the effect of the metallic cap size in the Wheeler cap method. It is finally demonstrated that the radiation efficiency of the DRA is significantly higher than that of the MSA at millimeter wave frequencies.Qinghua Lai, Georgios Almpanis, Christophe Fumeaux, Hansruedi Benedickter, and Ruediger Vahldiec

100-nm-Gate (Al,In)N/GaN HEMTs Grown on SiC With F-T=144 GHz

One-hundred-nanometer-gate (Al, In) N/GaN highelectron- mobility transistors (HEMTs) grown on semi-insulating SiC achieve a maximum current density of 1.84 A/mm at V-GS = 0 V, an extrinsic transconductance of 480 mS/mm, and a peak current gain cutoff frequency as high as f(T) = 144 GHz, which is the highest so far reported for any (Al, In) N/GaN-based HEMT. This f(T) matches the best published values that we could find for 100-nm-gate (Al, Ga) N/GaN HEMTs, thus closing the cutoff frequency gap between (Al, In) N/GaN and (Al, Ga) N/GaN HEMTs. Additionally, similar devices grown on (111) highresistivity silicon show a peak fT of 113 GHz, also setting a new performance benchmark for (Al, In) N/GaN HEMTs on silicon. Our findings indicate significant performance advantages for (Al, In) N/GaN HEMTs fabricated on SiC substrates. The improved performance for devices grown on SiC is derived from the superior transport properties of (Al, In) N/GaN 2DEGs grown on that substrate